This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7 119 from an application entitled COMPATIBLE OPTICAL PICKUP earlier filed in the Korean Industrial Property Office on the 23rd day of Oct. 1998, and there duly assigned Serial No. 44620/1998, a copy of which is annexed hereto.
1. Field of the Invention
The present invention relates to an optical process and apparatus for writing and reading on a variety of otherwise incompatible optical memories generally, and more particularly, to an optical pickup incorporating a planar lens having a stepped grating, capable of recording or reproducing information on or from a Compact Disc (CD) family media including a CD rewritable (CD-RW) and a Digital Versatile Disc (DVD, also called Digital Video Disc).
2. Description of the Related Art
We have found that the proliferation of varying optical media formats has created a need for a single apparatus compatible with the assorted optical media. Recently, there is a need for an optical recording and/or reproducing apparatus capable of recording and/or reproducing information on and/or from a DVD at a high density and be compatible with the CD family media such as CD, recordable CD (CD-R), CD-RW, CD interactive (CD-I) and CD plus graphics (CD+G). A single apparatus able to read and write all the varying formats is much more economical and efficient to use.
The standard thickness of existing CD family media is 1.2 mm, whereas the thickness of DVDs has been standardized to 0.6 mm in consideration of the allowable error in the tilt angle of a disc and the numerical aperture (NA) of an objective lens. Accordingly, when recording or reproducing information on or from a CD using an optical pickup for DVDs, spherical aberrations occur due to a difference in the thicknesses between these two types of discs. Such spherical aberration cannot provide a light intensity sufficient for recording an information (radio frequency) signal or may deteriorate the signal reproduced from the CD. Also, DVDs and CD family media utilize different wavelengths for light for reproduction. CDs use light having a wavelength of about 780 nm as a light source for reproduction, whereas DVDs use light having a wavelength of about 650 nm as a light source therefor. Thus, an optical pickup compatible with CDs, having an optical source capable of emitting different wavelengths of light, and a structure in which optical spots can be formed at different focal positions is required.
An exemplar of the prior art, Haruguchi et al. (U.S. Pat. No. 5,923,636, Optical Pickup, Jul. 13, 1999) discloses an optical pickup for recording on and reproduction from recording media of different recording densities such as CD and DVD. A diaphram means is used to vary the diameter of a light beam incident upon an objective lens. The objective lens is used to focus the beam on the media.
Kim (U.S. Pat. No. 5,930,219, Optical Pickup Device for Discs of Varying Characteristics, Jul. 27, 1999) discloses an optical pickup apparatus which is capable of reading data from and writing to discs of varying densities and thicknesses. The Kim ""219 patent controls the numerical aperture of an objective lens by using a Liquid Crystal Shutter (LCS) and a diffraction hologram. The diffraction hologram has gratings which are of uniform depth which diffracts certain types of light. The diffraction hologram alone is not enough to record and read CDs and DVDs. The added element of the LCS is necessary.
An object of the present invention is to provide an optical pickup capable of reading and writing on a variety of incompatible optical memory formats.
Another object of the present invention is to be able to read and write on optical media of differing thicknesses and densities.
Another object of the present invention is to avoid using a variable diaphragm in an optical pickup. A variable diaphragm is manufactured through a sophisticated and expensive process.
Another object of the present invention is to provide a compatible optical pickup capable of recording or reproducing information on or from digital versatile discs (DVDs) and compact disc (CD) family media including CDs, recordable CDs (CD-Rs) and CD rewritables (CD-RWs), by adopting a planar lens having a stepped grating, which directly and diffractingly transmits light incident thereto according to the wavelength of light.
These and other objects may be attained with a process and a compatible optical pickup that uses a first optical source for emitting a first light having a predetermined wavelength; a second optical source for emitting a second light having a long wavelength relative to the first light; a beam splitter that changes the traveling path of an incident light; an objective lens for condensing the first and second lights onto optical discs having different thicknesses, respectively; an optical diffractor having a first region which directly transmits the first and second light incident thereto, and a second region bounding the first region, that directly transmits the incident first light and diffractingly transmits the second light toward an optical axis; and a photodetector for sensing information signals and error signals from the first and second light which have been reflected by the optical discs and passed through the optical path changing means.
In another aspect of the present invention, there is provided a compatible optical pickup with a first optical unit including a first light source for emitting a first light having a wavelength of 650 nm, and a first photodetector for receiving the first light; a second optical unit including a second light source for emitting a second light having a wavelength of 780 nm, and a second photodetector for receiving the second light; a polarization beam splitter for changing the paths of the first and second light; an objective lens for condensing the first and second lights to form optical spots onto optical discs having different thicknesses; and an optical diffractor having a first region which directly transmits the first and second light incident thereto, and a second region bounding the first region, which directly transmits the incident first light and diffractingly transmits the second light toward an optical axis.